This invention relates to the filtration field, and more particularly, to an improved disposable vacuum filtration apparatus capable of detecting microorganisms and particulates in liquid samples. There are commercially available disposable vacuum filtration devices for detecting microorganisms and particulates in liquid samples available today. The currently available disposable vacuum filtration devices for detecting microorganisms and particulates in liquid samples contain a base section, a removable funnel section, and a removable lid. An absorbent pad, and microporous filter are inserted into the base section. The absorbent pad is placed into a well in the base section, and the microporous filter (normally of larger diameter than the absorbent pad) is inserted above the absorbent pad (i.e. on the upstream side of the absorbent pad). The absorbent pad provides support for the microporous filter. The base section also contains a filter support means which provides support for the absorbent pad and provides fluid flow communication between the downstream side of the absorbent pad and an outlet port located at the bottom of the base section. The removable funnel section is press fitted or snapped into the base section. The outer periphery of the microporous filter is either sealed to the base section or sealed between the bottom edge of the funnel section and the base section. The removable lid is press fitted onto the top of the removable funnel section preferably with a fit that allows easy removal, but that does not allow the lid to accidentally separate from the funnel section. These devices are normally sold pre-sterilized. In use the end user preferably removes a sterile vacuum filtration device from its shipping package in a laminar flow hood to prevent contaminating the device. The lid is then removed from the funnel section and a liquid sample to be tested is poured into the funnel section. The lid is then placed back onto the funnel section and the outlet port of the base section is connected to a vacuum means. The vacuum means sucks the liquid through the microporous filter, and through the absorbent pad, and then through the outlet port, into the vacuum means. Either the lid or the funnel section contains a venting means to allow air to replace the liquid in the funnel as vacuum removes the liquid from the funnel. Once all of the liquid sample has been sucked from the vacuum filtration device, the user will remove the vacuum filtration device from the vacuum means, and then remove the lid from the funnel section, and then remove the funnel section from the base section, and then place the lid onto the top of the base section, and then discard the funnel section. The lid should fit onto the top of the base section with a press fit that allows easy removal, but that does not allow the lid to accidentally separate from the base section when the base section is inverted. With the funnel removed, and with the lid attached to the top of the base section, the lid, base section assembly becomes a petri dish. Either the lid or base section should contain a venting means to allow the air in the interior of the base section with the lid attached to communicate with air outside of the base section during the incubation cycle. However in some applications it is desirable that the lid be tightly sealed to the base during the incubation cycle. The user then adds a quantity of growth media to the outlet port of the base section, so that the absorbent pad becomes saturated with growth media. The outlet port of the base section is then plugged with a plug (normally supplied with the device), and the base section with lid and plug is inverted and placed into an oven to incubate, so that any bacteria that was trapped on the upstream side of the microporous filter will grow into colonies to be counted later.
When it is desired to count particles in a liquid sample (for example glass fragments in a soft drink sample), the above steps of adding growth media, and incubation are not necessary. The particles can be counted on the upstream side of the microporous filter once the liquid sample has been filtered through the microporous filter. The microporous filter may contain a grid on its upstream side as an aid in counting either particles or microorganisms.
The currently available vacuum filtration devices for detecting microorganisms and particulates in liquid samples suffer from the following drawbacks:                a) The bottom portion of the funnel section is press fitted to the base section, therefore the outside diameter of the funnel section must match the inside diameter of the base section. This means that the disposable molded parts must be molded to a very high tolerance, which leads to part matching (i.e. funnel sections being individually matched to base sections), high scrap rates, and higher production costs.        b) The lid is press fitted to the top of the funnel section, and to the top of the base section, therefore the outside diameter of the top of the funnel section, and the outside diameter of the top of the base section must match the inside diameter of the lid. Again this means that the disposable molded parts must be molded to a very high tolerance, which leads to part matching (i.e. funnel sections and base sections being individually matched to a lid), high scrap rates, and higher production costs.        c) For different applications different membrane filter types must be used. The different membrane filter types may be of different thickness. Therefore a funnel section, base section matched pair that works with one type of filter may not work with another type of filter.        d) When the membrane filter wets during filtration, it will swell. The currently available devices do not provide a means to keep the swelled filter to remain in intimate contact with the absorbent pad. If the swelling causes the membrane filter to lift away from the absorbent pad, bacteria that is present on the upstream side of the membrane filter in the area that has lifted away from the absorbent pad will not grow when incubated. Therefore, these bacteria will not be detected.        e) All of the above limitations of the present art are exasperated when parts are molded from materials such as polypropylene or polyethylene, which are difficult to mold to tight tolerances.        f) In some applications it is necessary to remove the membrane filter from the base section after filtration is complete, and place said membrane filter into another petri dish for incubation. Currently available devices do not provide an easy means to remove the wet membrane filter from the base section.        
It is therefore an object of the present invention to provide a disposable vacuum filtration apparatus for detecting microorganisms and particulates in liquid samples that can be assembled from component parts that have been molded to normal tolerances (i.e. all component parts to be molded within a dimensional tolerance range of ±0.004 of an inch or better). Another object of the present invention is to provide a disposable vacuum filtration apparatus for detecting microorganisms and particulates in liquid samples that can use a filter means of varying thickness, while providing a positive seal to prevent the microorganisms from bypassing the filter means. Another object of the present invention is to provide a disposable vacuum filtration apparatus for detecting microorganisms and particulates in liquid samples that provides a means to keep the downstream side of the filter means in intimate contact with the upstream side of the absorbent pad disposed below it when the filter means and absorbent pad are both wet. Another object of the present invention is to provide a disposable vacuum filtration apparatus for detecting microorganisms and particulates in liquid samples that can be molded from materials such as polypropylene, or polyethylene, or from a combination of materials such as polypropylene and polystyrene. Another object of the present invention is to provide a disposable vacuum filtration apparatus for detecting microorganisms and particulates in liquid samples wherein the filter means can be sealed to the base in a manner that will prevent bypass of the microorganisms around the filter means. Another object of the present invention is to provide a disposable vacuum filtration apparatus for detecting microorganisms and particulates in liquid samples wherein the filter means can be sealed using a compression seal between the base and the funnel in a manner that will prevent bypass of the microorganisms around the filter means.